Generally speaking, a Micro-Electromechanical System (MEMS) is a highly miniaturized device having both electrical and mechanical components. MEMS devices are typically fabricated on or from a substrate material, such as silicon or polysilicon. Various electrical and mechanical structures are formed using a variety of techniques.
The mechanical structures of the MEMS are typically very fragile, and can be easily damaged. Furthermore, the mechanical structures of the MEMS are typically very sensitive, and can be easily impeded. Many things can affect MEMS performance, including dirt, moisture, and even static electricity.
Therefore, a cap is typically placed over substantially all of the MEMS mechanical and electrical components in order to protect the mechanical and electrical components of the MEMS. The cap typically includes a cavity for protecting the MEMS structures. For convenience, this cavity is referred to hereinafter as the MEMS cavity. The cap is bonded onto the MEMS in such a way that the MEMS structures to be protected are positioned within the MEMS cavity.
MEMS devices are typically produced by forming the electrical and mechanical components for multiple MEMS devices on a single MEMS wafer, forming the MEMS cavities for multiple caps on a single cap wafer, bonding the cap wafer onto the MEMS wafer, and mechanically cutting through both the MEMS wafer and the cap wafer to separate the individual MEMS devices. The resulting caps cover substantially all of the MEMS electrical components (except, perhaps, electrical bond pads for making electrical connections to the MEMS device). This is due in part because the separation of the individual MEMS devices must be done in such a way that the mechanical cutting does not cut through the MEMS electrical components.